1. Field of the Invention
The present invention relates to an ophthalmic optical apparatus for observing and treating an eye, and more particularly to an ophthalmic optical apparatus having an alignment optical system for treating the eye.
2. Related Background Art
For a series of ophthalmic diseases including, inter alia, retina disease, a high density laser radiation or a so-called photo-coagulation laser is used to treat a diseased part and it is irradiated to the diseased part as a light spot. An irradiation output, an irradiation time and a spot size of the photo-coagulation laser are varied depending on a photo-coagulation operation to a particular diseased part. It is very important to focus the photo-coagulation laser to the diseased part, and to this end a proper alignment system is required. In a prior art alignment system, an alignment beam to be used for the alignment is split into two or more light beams which are collected and combined to attain exact focusing.
For example, in an ophthalmic optical apparatus (laser photo-coagulation apparatus) for observation and treatment which uses a laser, disclosed in U.S. Pat. No. 4,499,897, particularly in FIG. 5 thereof, an alignment laser beam 22 which is a visible ray generated by a laser oscillator 21 in the laser photo-coagulation apparatus 20 is split into two parallel light beams 22a and 22b by a pair of semi-transmissive prisms (beam splitter) 23, and those light beams pass through a first beam splitter (dichroic mirror) 24, are reflected by a ring-shaped outer periphery of a second beam splitter (dichroic mirror) 25 and directed to an object (an eye of a patient), not shown, through a focusing lens 26 so that they are focused on the object plane.
In this case, an in-focus state is attained at a point where the two light beams 22a and 22b coincide. When they are focused on the object plane, one spot pattern h is formed, and when they are not focused, two spot patterns g and i are formed.
On the other hand, a photo-coagulation light 29 for treatment which is generated by another laser oscillator 28 passes through a beam expander 30 so that it is expanded to a light beam having a diameter which is slightly smaller than a gap between the two alignment light beams 22a and 22b. The expanded photo-coagulation light is reflected by the first beam splitter (dichroic mirror) 24, follows the same light path as that of the alignment laser beam 22, is further reflected by the second beam splitter 25 and is directed to the object through the focusing lens 26 so that it is focused at the coincident point of the two beams 22a and 22b of the alignment laser beams 22, that is, at the same point as the point on the object plane at which the spot pattern h is formed.
In the laser photo-coagulation apparatus 20, the prism 23 is rotated so that the two light beams 22a and 22b are rotated around an optical axis of the photo-coagulation light 29. When the photo-coagulation light 29 is generated by the laser oscillator 28 after the in-focus state has been confirmed, the photo-coagulation light 29 follows the same light path as that of the alignment laser beam 22 and it is focused at the same point as the point on the object plane at which the spot pattern h of the alignment laser beam 22 is formed in the in-focus state so that the diseased part is treated.
In the prior art ophthalmic optical apparatus (laser photo-coagulation apparatus) for observation and treatment, since the two alignment light beams 22a and 22b which go along the outer periphery of the photo-coagulation light 29 are rotated around the optical axis of the photo-coagulation light 29, the construction is complex, a relatively long time is required for the alignment, the process to generate the photo-coagulation light 29 is complex and a long time is required for the treatment.
U.S. Pat. No. 4,917,486 discloses a laser photo-coagulation apparatus in which, instead of rotating the two alignment light beams, a mask having four apertures centered at an optical axis and arranged at an angular pitch of 90.degree. is provided on an alignment light path of a collimated light beam, the four collimated light beams transmitted through the apertures of the mask are used as the alignment light beams which go along the outer periphery of the treatment light beam, and the in-focus state on the object plane is determined by the coincidence state of the four spot patterns formed by the four light beams.
However, in the laser photo-coagulation apparatus disclosed in U.S. Pat. No. 4,917,486, only those portions of the light generated by the alignment light source which are transmitted through the four apertures formed in the mask can be used as the alignment light beams and hence energy is wasted.
In the alignment system of the prior art laser photo-coagulation apparatus, the light beam is split into two or four parallel alignment light beams by the prism and they form the predetermined spot pattern at the in-focus state to permit the detection of the in-focus state. However, the position precision of the prism is hard to attain. Further, the entire construction of the optical system is complex and the prism cost is expensive.